Method and Apparatus For Data Communication Utilizing The North American Terrestrial System

ABSTRACT

A method and apparatus for enhancing the current data communication capabilities of the North American Terrestrial System (NATS) Network is presented. In accordance with an embodiment of the present invention, an airborne data server (ADS) is added to the airborne architecture of the current NATS Network and a ground data gateway (GDG) is added to the ground-based architecture of the current NATS Network. The ADS functions as a router/gateway connected to many local area networks (LANs) aboard the aircraft. The ADS provides for the automation of data services such as scheduling, routing and translation. The GDG is the central hub for the network and dispatcher of data to customer premises or to the aircraft.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No.60/106761 filed Nov. 3, 1998, entitled “A New Approach To DataCommunications Utilizing the North American Terrestrial System.”

BACKGROUND

The present invention relates to data communication between an aircraftand a ground-based destination device. More particularly, the presentinvention relates to a method and apparatus for enhancing the currentdata communication capabilities of the North American Terrestrial System(NATS) Network.

Current data service offerings to commercial aircraft are limited infunction and capability. One of the known systems for transmitting datato and from an aircraft is the Aircraft Communication Addressing andReporting System (ACARS). The ACARS system is primarily used to transmittwo types of data. The first type of data is known as safety data.Safety data is transmitted from the pilot/flight crew to the tower orthe dispatch and includes information such as the aircraft's heading andthe aircraft's altitude. The second type of data is known asoperational/administrative data. Operational/administrative data istransmitted from the aircraft to the dispatch and may include, forexample, information which indicates when particular equipment aboardthe aircraft is in need of repair.

The ACARS system typically comprises an ACARS management unit (MU) and avery high frequency (VHF) transceiver. In general terms, the ACARS MUcollects aircraft data from various sources aboard the aircraft (such asavionics equipment) and sends the collected data to the VHF transceiver.The VHF transceiver encapsulates the data in accordance with a protocol,modulates a frequency channel using the encapsulated data, and transmitsthe modulated frequency channel to the control tower or the dispatch.Upon successfully receiving data, the tower or the dispatch uses afrequency channel to transmit an acknowledgment message to theoriginating aircraft.

There are several drawbacks associated with the ACARS system. First, thenumber of channels available for transmitting data is limited. Thegeographic region of the United States is subdivided into a number ofAir Traffic Control (ATC) regions. Each ATC region is allocated only onechannel for ACARS system transmissions. Thus, each ACARS equippedaircraft within a particular ATC region must share the same channel.

A second drawback is that the ACARS system is limited to transmittingshort messages. The system is not suitable for transmitting files ofdata to and from an aircraft. Third, the ACARS system is not intendedfor public correspondence. Thus, passengers aboard an aircraft areunable to use ACARS to transmit data from the aircraft.

Another drawback associated with the ACARS system is that the systemlacks an encryption method. Some of the data transmitted to and from theaircraft is considered sensitive. One example of such sensitive data isaircraft performance data. Aircraft performance data may includeparameters such as engine vibration, engine temperature, and whether ornot the tail of the aircraft was dragged across the ground during atake-off or a landing. This type of information is considered sensitivebecause it could be used to indicate that the pilot did something wrongwhile flying the aircraft.

Finally, the ACARS system implements protocols which, although widelyused within the aviation community, are incompatible with commercial“off the shelf” software and protocols. The use of these protocols makesit difficult to develop new application software to run over the ACARSdata link. Further, system enhancements and upgrades are difficultbecause there are a limited number of software developers/engineersfamiliar with how the ACARS protocols are implemented.

Another known system which provides limited data communication betweenan aircraft and a ground station is known as the North AmericanTerrestrial System (NATS) Network. The NATS Network comprises a NATSradio set aboard each subscribing aircraft and more than 150 AT&T Corp.NATS ground stations strategically located throughout the continentalU.S., Canada, and Mexico in order to provide full coverage tosubscribing aircraft at cruise altitude. Each of the over 150 groundstations are connected to both a public switched telephone network(PSTN) and a wide area network (WAN). In addition, micro-cell groundstations are deployed at key airports to provide localized groundcoverage to aircraft on the tarmac or at the gate.

Aboard each subscribing aircraft, a plurality of telephone handsets areadapted to be connected to each NATS radio set. These telephone handsetsare adapted to facilitate connecting a device such as a laptop computerto the NATS radio set. Passengers may use the telephone handsets toexchange voice information with ground-based telephones via the NATSradio set, the ground stations and the PSTN. Similarly, passengers mayexchange data with ground-based systems via the NATS radio set, theground stations and the WAN.

The NATS radio set operates in the UHF range. The air-to-ground transmitband is located between 894 and 896 MHZ. The ground-to-air band isbetween 849 and 851 MHZ. Each band is broken into 10 channel blockswhich contain 29-6 kHz wide user channels (one for uplink and one fordownlink). Additionally 63.2 KHz wide control channels (a.k.a. pilotchannels) are available in each channel block. Each ground station isassigned one of the 10 channel blocks. These pilot channels are used bythe ground station to broadcast frequency availability and sundry otherstatus and control messages to the airborne radios. One of the sixavailable pilot channels is assigned to each service provider. Thus,aircraft flying over a geographic region served by a particular groundstation may exchange voice and data information with ground-basedsystems using one of the 29 channels available to that ground station.

Unfortunately, the NATS Network is primarily intended to facilitatevoice (rather than data) transmission to and from an aircraft. NATSvoice and data transmissions are implemented in accordance with atechnique known as circuit mode. In circuit mode, one telephone handsetor one laptop computer connected to a telephone handset aboard asubscribing aircraft may exchange voice or data information with oneground-based destination device using one available NATS channel. Eachuser aboard an aircraft is assigned one channel for the duration of thetime they are transmitting and receiving information.

As a subscriber aircraft flies over a geographic region, the NATS radioset continuously monitors the signal strength from the available groundstations and transmits data to the ground station which is currentlyproviding the strongest signal strength. In circuit mode, the process ofswitching ground stations breaks the transmission link between theaircraft and the ground station. Thus, data transmission is interruptedduring the switching process.

Circuit mode transmission may be contrasted with a technique known aspacket mode. In accordance with packet mode, multiple users aboard anaircraft might share a singe channel to transmit data to multipledifferent destination addresses. Due to circuit mode implementation andother NATS Network constraints, only a limited number of users aboardany one aircraft may simultaneously make telephone calls from theaircraft and only a limited number of users aboard any one aircraft maysimultaneously use their laptop computers to transmit and receive datafrom the aircraft.

Thus, there is a need for a method and apparatus which solves the abovedescribed problems.

SUMMARY OF THE INVENTION

Current data service offerings to commercial aircraft are limited infunction and capability. Customers such as airlines are seekingalternatives to enhance data capabilities to and from the aircraft whileintegrating it into their information network. Of course, any solutionproposed must be cost effective as well as technically capable.

The present invention is a method and apparatus which utilizes the AT&TNorth American Terrestrial System (NATS) Network to provide enhanceddata capability for customers to support data traffic to or from theaircraft. An OSI-based approach is utilized for the presentation thatincludes stack definition at each network node. In accordance with anembodiment of the present invention, an on-board network architecture iscentralized around an Airborne Data Server (ADS). The ADS is arouter/gateway connected to many on-board LANs that provide automationof data services (scheduling, routing, translation). Also in accordancewith the present invention, an embodiment includes an air-to-grounddigital cellular radio network (AT&T NATS), which utilizes a token-basedforwarding scheme based on IP packets. Mobility is also an importantaspect of the present invention. The benefits of the present inventioninclude enhanced data rates, security, quality of service reliability,and service type (short message vs. block transfer).

In accordance with an embodiment of the present invention, a Ground DataGateway (GDG) is the central data hub for the network and dispatcher ofdata to customer premises equipment or to the aircraft. In anotherembodiment, the AT&T NATS data network is used to support backchannel(uplink data requests) communications in conjunction with a highbandwidth forward channel (downlinking HTTP, large files, etc.) for highbandwidth systems. The present invention also supports transportingvoice over Internet protocol (IP) networks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a network suitable for practicing anembodiment of the present invention.

FIG. 2 is a block diagram of an example of an airborne systemarchitecture which may be installed in a subscriber aircraft inaccordance with an embodiment of the present invention.

FIG. 3 is a block diagram of a North American Terrestrial System (NATS)radio set modified in accordance with an embodiment of the presentinvention.

FIG. 4 is a block diagram of an airborne data server (ADS) in accordancewith an embodiment of the present invention.

FIG. 5 is a block diagram of a ground data gateway (GDG) in accordancewith an embodiment of the present invention.

FIG. 6 illustrates an example of the flow of data involved in deliveringa weather map to an airborne application terminal aboard a subscribingaircraft in accordance with the present invention.

FIG. 7 illustrates an example of the flow of data involved in deliveringdata from a subscribing aircraft to the dispatch in accordance with thepresent invention.

FIG. 8 illustrates an example of the flow of data involved in exchangingdata between a laptop utilized by a passenger or crew member and aground-based computer in accordance with the present invention.

FIG. 9 illustrates an example of the flow of data involved in completinga telephone call in accordance with the present invention.

DETAILED DESCRIPTION

The present invention enhances the data services currently offered tocommercial aircraft by modifying the current AT&T North AmericanTerrestrial System (NATS) Network. As mentioned above, the current NATSNetwork is primarily intended to facilitate voice (rather than data)transmission to and from an aircraft. In accordance with an embodimentof the present invention, the current capabilities of the NATS Networkare enhanced by adding an airborne data server (ADS) to the airbornearchitecture of the current NATS Network and by adding a ground datagateway (GDG) to the groundbased architecture of the current NATSNetwork. This embodiment eliminates the above-described ACARS systemsingle channel sharing constraint by enabling subscribing aircraftwithin a particular ATC region to transmit data (and/or voice)information by selecting from among the 29 channels currently utilizedby NATS Network radio sets. Among other features (described in greaterdetail below), the ADS and GDG of the present invention also enable thecurrent NATS Network to support the following new services: 1) thepacket-mode-based transmission of voice and or data information, 2) thetransmission of files of data to and from subscribing aircraft, 3)expanded public correspondence services, 4) an encryption method toprotect transmitted voice or data information from unauthorized access,and 5) the implementation of protocols which are compatible withcommercial off-the-shelf software and protocols.

The high level goal of the present invention is to provide a seamlesstransmission control protocol/Internet protocol (TCP/IP) network tosubscribing customers by enhancing the currently known capabilities ofthe NATS Network. One of the foundations for a network in accordancewith the present invention is AT&T's patented IP addressing scheme forground stations and airborne radios. The method and apparatus of thepresent invention provides customers such as airlines with analternative to traditional data services. By using standard Internetprotocols such as TCP/IP, customers implementing a data network inaccordance with the present invention are able to enjoy the manybenefits of a modem wide area network (WAN) for their operational andmaintenance communications needs. Since TCP/IP is a commerciallyaccepted protocol with a large base of applications, it is possible toprovide new services in a timely and more cost efficient manner thanpreviously possible.

Networks in accordance with the present invention also include the addedbenefits of security, mobility, a dedicated channel (for higherthroughput), and a reliable network transport that offers an attractiveoption for air-to-ground and ground-to-air data needs.

FIG. 1 is a block diagram of a network suitable for practicing anembodiment of the present invention. In FIG. 1, each subscribingaircraft 102 is flying within proximity of a ground station 104. Eachground station 104 may be, for example, a tower equipped with an antennafor transmitting and receiving radio frequency signals. Although twosubscribing aircraft and two ground stations 104 are illustrated in FIG.1, the present invention may include a greater or lesser number ofeither. Each subscribing aircraft includes an airborne systemarchitecture which will be described below with reference to FIG. 2. Theairborne system architecture aboard each subscribing aircraft 102 andeach ground station 104 are adapted to communicate using one or more ofa plurality of system frequencies.

FIG. 1 also illustrates a WAN adapted to connect each ground station 104to a ground data gateway (GDG) 110. GDG 110 may be, for example, ageneral purpose computer. An example of a GDG will be described in moredetail below. FIG. 1 also illustrates each ground station 104 adapted tobe connected to a public switched telephone network (PSTN) 108.Additionally, a call switching center (CSC) 112 is adapted to beconnected to PSTN 108.

FIG. 2 is a block diagram of an example of an airborne systemarchitecture which may be installed in a subscribing aircraft inaccordance with an embodiment of the present invention. In FIG. 2, aNATS radio set 202 is adapted to be connected to an airborne data server(ADS) 204. NATS radio set 202 is a known device manufactured by the AT&TCorp. hi accordance with the present invention, this known device ismodified in software and hardware as illustrated in greater detailbelow. ADS 204 may be a general purpose computer and will also bedescribed in greater detail below. ADS 204 is adapted to exchange datainformation with other aircraft systems/components (not shown in FIG. 2)such as an Aircraft Condition Management System (ACMS) or an aircraftdiscrete. ADS 204 is also adapted to be connected to one or more localarea networks (LAN's) such as ethernet 210. In FIG. 2, two printers 212(one in the aircraft cabin and one in the aircraft flight deck) andthree general purpose computers 214 (two distributed in the aircraftcabin and one in the aircraft flight deck) are each adapted to beconnected to ADS 204 via ethernet 210. A greater or lesser number ofprinters and general purpose computers may be included in the systemarchitecture in accordance with the present invention.

FIG. 2 also illustrates five telephone handsets 206 adapted to beconnected to NATS radio set 202. A laptop computer 208 is adapted to beconnected to NATS radio set 202 via a telephone handset 206. Voice ordata information from one of handsets 206 may be sent to ADS 204 viaNATS radio set 202. Voice or data information to one of handsets 206 maybe received from ADS 204 via NATS radio set 202.

The method for providing data communications services in accordance withthe present invention will now be described in general terms withreference to FIG. 1 and FIG. 2. To transmit data from a subscriberaircraft 102 to a ground-based destination device, ADS 204 receivesvoice or data information as appropriate) from one or more of thevarious sources described above and encapsulates the voice or datainformation into packets in accordance with a protocol such as TCP/IP.These TCP/IP encapsulated packets are then sent to NATS radio set 202.NATS radio set 202 then modulates a system frequency using theseencapsulated data packets and transmits the modulated signal through theair to the ground station currently providing the strongest signal tothe NATS radio set aboard the originating subscriber aircraft 102. Thereceiving ground station 104 demodulates the received signal to recoverthe encapsulated packets and sends these packets to GDG 110. GDG 110routes either the received data packets, the data included within thedata packets or the received data encapsulated in accordance withanother protocol (such as X.25) to the appropriate ground-baseddestination device. This destination device may be, for example, ageneral purpose computer (not shown in FIG. 1) adapted to be connectedto GDG 110, a general purpose computer (not shown in FIG. 1), adapted tobe connected to GDG 110 via a network such as the Internet, or atelephone adapted to be communicated to GDG 110 via PSTN 108.

A subscriber aircraft 102 may also receive voice or data information(whether or not in response to a query from the aircraft). The voice ordata information from a ground-based device (not shown in FIG. 1) isreceived at GDG 110. GDG 110 then determines which ground station 104 iscurrently servicing the subscriber aircraft 102 on which the destinationdevice is located. GDG 110 then encapsulates the received voice or datainformation in accordance with a protocol such as TCP/IP and sends thedata packets to the determined ground station 104. The ground station104 modulates a system frequency using the received data packets andtransmits the modulated signal through the air to the aircraft on whichthe destination device is located. The modulated signal is received bythe NATS radio set 202 aboard the aircraft. The NATS radio setdemodulates the received signal and sends the data packets to the ADS204. ADS 204 sends either the received data packets, the data withinthese packets or the data encapsulated in accordance with anotherprotocol to the intended destination device. Examples of the destinationdevice may include another aircraft system, a telephone handset 206, alaptop computer 208 or computer(s) 214.

Some of the above described components of the present invention and morespecific examples of how the method and apparatus of the presentinvention may be implemented to provide data services to an aircraftwill now be described.

FIG. 3 is a block diagram of an AT&T North American Terrestrial System(NATS) radio set modified in accordance with an embodiment of thepresent invention. In FIG. 3, a NATS radio set 302 comprises a processor304 adapted to be connected to a computer readable memory segment 306and an ethernet card 310. Computer readable memory segment 306 storescomputer program code segments which, when executed by processor 304,implement the NATS radio set functions described throughout thisdocument. These computer program code segments are included within oneNATS module 308. Although in this embodiment of the invention thecomputer program code segments are shown in one module, it can beappreciated that this module can be further separated into more modulesand still fall within the scope of the invention.

In general terms, the computer program code segments within NATS module308 perform the following functions which will be described in moredetail below: 1) modulate a system frequency using data packets receivedfrom the ADS and transmit the modulated signal to a ground station; 2)demodulate signals received from ground stations to obtain the datapackets included within these signals and send these data packets to theADS; 3) implement procedures for switching between ground stations; 4)queue data packets received from the ADS, as necessary, during switchingoperations; and 5) seize a system channel in response to receiving apage from a ground station using a pilot channel.

FIG. 4 is a block diagram of an airborne data server (ADS) in accordancewith an embodiment of the present invention. In FIG. 4, an ADS 404comprises a processor 402 adapted to be connected to a computer readablememory segment 406. Computer readable memory segment 406 stores computerprogram code segments which, when executed by processor 402, implementmany of the ADS functions described in this document. These computerprogram code segments are included within an ADS module 408. Although inthis embodiment of the invention the computer program code segments areshown in one module it can be appreciated that this module can befurther separated into more modules, and still fall within the scope ofthe invention.

In general terms (for air-to-ground transmissions), the computer programcode segments of ADS module 408 receive voice or data information froman aircraft system or device, encapsulate the voice or data informationinto packets in accordance with a protocol such as TCP/IP and send theseencapsulated data packets to a NATS radio set. In general terms (forground-to-air transmissions), the computer program code segments of ADSmodule 408 receive TCP/IP encapsulated packets from a NATS radio set202, remove the encapsulation and send the packets to the appropriateaircraft system or aircraft device. Other ADS functions which may beimplemented using ADS module 408 will be described below.

The ADS provides data communications services for airline operationalinformation (e.g., maintenance and operations communications) as well asnew data applications targeted directly for the passenger. The ADSprovides the core communications functions of the present invention. TheADS provides both on-board and off-board communications.

On the on-board side, the ADS provides connection to passengers usingthe cabin distribution system, as well as to the flight crew andmaintenance personnel using application terminals on Ethernetconnections. Connection to avionics equipment is via, for example,Aeronautical Radio Incorporated (ARINC) 429, 573 or 646 and avionicsdiscrete interfaces.

On the air-to-ground side, the ADS may communicate using various meansincluding connections via direct or wireless Ethernet, AT&T NATSconnections, or SATCOM Data3. While several communications paths are orwill in the near future be available aboard aircraft, the cornerstone ofthe present invention is the air-ground link provided by the AT&T NATSNetwork.

In one embodiment, the ADS relies on commercial operating systemsoftware and AT&T provided communications system software to provide theoverall functionality of the system.

In one embodiment, the ADS may include the following components: anARINC-429 and discretes card, Single Board Computer, a power supply, amass storage and a custom filtering/interface card. All applications maybe built upon a commercially available operating system.

In one embodiment, the ADS is packaged in a 6 MCU, ARINC 600 packageutilizing forced air cooling. The ADS relies largely on the use ofcommercial off-the-shelf (COTS) hardware, taking advantage of theeconomy of scale of design that is enjoyed by the commercial PC marketpresently.

The Airline Electronic Engineering Committee (AEEC) has establishedproject number 645 under the Systems Architecture and Interfaces (SAI)subcommittee to create an ARINC specification for the Airborne FileServer architecture. Several airlines have historically expressedinterest in an Airborne File Server but have been reluctant to sign upwithout an underlying ARINC specification. The goal of the SAI-645subcommittee will be to define a footprint and pin definition forAirborne File Servers.

In one embodiment of the present invention, the ADS provides means forpassengers to access data using the existing AT&T cabin telephonesystem. To use the interface, the passenger accesses the ADS byconnecting his or her laptop to the RJ-11 connector on the base of thehandset or in the handset cradle. Passengers are able to attain ahigh-speed connection (up to 56 kbps with today's modems) into the ADS.In this embodiment of the present invention, the ADS behaves as anInternet Service Provider (ISP), providing logon and authentication andcan serve out content through an on-board Intranet. In one embodiment ofthe present invention, the ADS includes at least one modem which isutilized to exchange data between the ADS and a modem within a laptopcomputer or general purpose computer.

The ADS may be pre-loaded with static data while on the ground. Thisdata may be data that the airline deems to be usable or interesting topassengers while in flight. (Example content might be the airline's homepage and accompanying links, details of the flight's destination city orsky mall type shopping.) Timely data, such as sports scores and stockquotes, may be uploaded to the aircraft on a periodic basis while inflight. The majority of user transactions in this embodiment do notrequire an air-ground link. When a user action does require anair-ground link (i.e., a shopping transaction occurs or an e-mailaccount needs to be accessed), the ADS routes the traffic through theAT&T NATS radio set allowing the transaction to complete. This approachprovides high-speed access for the user to obtain data using publiclyaccepted methods of interconnecting. Additionally, this embodimentrequires no modifications to the existing aircraft telephone cableplant. For example, a private branch exchange (PBX) (used in oneembodiment of the present invention to provide switching functionsbetween the plurality of handsets and the ADS) is currently includedwithin either the NATS radio set or a cabin telephony unit (CTU) of theexisting aircraft telephone cable plant.

FIG. 5 is a block diagram of a ground data gateway (GDG) in accordancewith an embodiment of the present invention. In FIG. 5, GDG 510comprises a processor 502 adapted to be connected to a computer readablememory segment 504. Computer readable memory segment 504 stores computerprogram code segments which, when executed by processor 502, implementmany of the GDG functions described throughout this document. Thesecomputer program code segments are included within one GDG module 508.Although in this embodiment of the invention the computer program codesegments are shown in one module it can be appreciated that this modulecan be further separated into more modules, and still fall within thescope of the invention.

Using GDG module 508, the GDG routes IP packet traffic (for example,data encapsulated in accordance with TCP/IP) to and from the airborneADS. A core function of the GDG is maintenance of route information sothat the GDG can forward IP packets to the correct ground station toservice a particular ADS. The GDG may also include firewalled links tothe Internet and corporate information systems.

Each IP packet from an ADS may be encapsulated in a private messageformat that includes information which allows the GDG to validate it.For instance, the airline and aircraft identifier of each ADS may beincluded in every message exchanged by the ADS and GDG. Validationprovides the ability to enable/disable features for a particular ADSbased upon the requirements of the customer. In addition, thisvalidation information allows the GDG to maintain state and billinginformation for each ADS on a per-message basis.

The GDG may also act as a centralized point for accounting purposessince each IP packet between an ADS and a final destination host mustpass through it. As a packet passes through the GDG, each ADS can beidentified by its unique address, thereby providing a per-ADSstatistical accounting capability. Additionally the length of eachmessage may be recorded so that the data exchanged can be accounted forwith granularity to the nearest byte (if so desired). In the unlikelyevent that a message is lost over the radio link, the ground station cannotify the GDG of the loss so that the statistics recorded can beproperly adjusted.

The GDG may also make use of a number of security techniques to protecta network in accordance with the present invention. First, the GDG'sconnection to hosts outside the network may be firewalled behinddedicated servers. These firewalls allow for IP address and portfiltering.

Secondly, all messages exchanged between the ADS and GDG may beencrypted to provide a secure radio link. The only entry points to thenetwork may be behind the ADS's onboard LAN or behind the GDG'sfirewall.

Thirdly, each message exchanged between the ADS and end destination maypass through the GDG's message engine where its source/destination IPaddress and port numbers can be validated. This provides the ability toturn on trusted services to trusted hosts while disabling untrustedservices and/or hosts.

In a scheme analogous to corporate Internet proxies, the GDG maymanipulate the source IP address of each packet as it leaves the presentinvention network for the Internet. In doing so, each packet from an ADSappears to come from the GDG when it arrives at the destination host.Similarly, packets destined to return to the ADS may be addressed to theGDG. This protects the true identity of hosts behind the GDG (i.e., ADS)from untrusted hosts on the Internet.

A number of ground-based hosts may serve in a supporting role to theGDG. These hosts are referred to as packet data application servers. Abrief description of their services is provided herein.

A real-time application server may be used for transactions that requireimmediate processing. For instance a Post Office Protocol 3 (POP3)e-mail server would allow for real-time retrieval of e-mail messagesfrom a ground server. Another service that could make use of thereal-time application server would be a credit transaction processingservice. This service could provide onboard credit card validation usingground-based validation servers.

A store and forward application server may provide an efficient means ofsending data to an ADS. A subscribing airline can have data sent to anADS by first transferring the data to the store and forward server. Thisserver is then responsible for contacting the GDG to establish a link tothe destination ADS. Once this is accomplished, the store and forwardserver can transfer the data over the present invention network. Pushingthe data transfer details back to the store and forward server veils thedetails of reaching an ADS from the host which initiated the datatransfer. For instance, if an ADS is currently unavailable (i.e.,because it is out of radio contact or the aircraft is powered down), theapplication server can hold on to the data until such time that it canbe delivered.

Many applications of interest make use of pre-packaged data. Forinstance weather, news, sports, etc. will need to be updatedperiodically and be available immediately when requested by an ADS.Since this information is likely to be requested by numerous ADSs it canbe cached by an application server and provided instantly whenrequested.

In the airline information systems arena, data exchanged between theaircraft and ground systems are often formatted in legacy formats.Furthermore the networks used are often older technologies (i.e., X.25).To facilitate serving this kind of data need, the GDG can employapplication servers which format data for legacy systems. This allowsthe present invention network to service customers in a manner whichthey are accustomed to while enjoying the advances of a modem network.

The physical layer of a NATS radio set modified in accordance with thepresent invention is implemented using a full-duplex digital modulationscheme. The channel is encoded with a forward error correction (FEC)scheme applied to scrambled, interleaved data frames. The data framescan contain voice, voice band data, or packetized data traffic.

The link layer of the data service may be implemented using a LinkAccess Protocol Balanced (LAPB)-inspired High Level Data Link Control(HDLC) layer called Radio Link Protocol (RLP). This layer includes suchfunctionality such as:

-   -   Sliding window flow control    -   Selective repeat automatic repeat request (ARQ)    -   CRC data protection

The RLP Frame size fits within the limitations of the existing AT&T NATSradio's physical layer frame size. Due to this sizing constraint, RLP isresponsible for fragmenting larger packets from higher layers.

The Packet Data Protocol (PDP) provides a peer-to-peer layer between theair and ground radios for reliable, sequenced delivery of packets.Packets consist of multiple frames from the RLP layer. Combinedtogether, these frames form an atomic message that is fit forconsumption by the edge servers (ADS and GDG).

The messages that are transferred across the radio link by the PDP layercontain IP packets encapsulated into a proprietary message format. Themessage structure may contain a number of fields such as:

-   -   Message Type    -   Message Length    -   Airline/Aircraft ID    -   User Data    -   Status

These fields allow the PDP layer to provide the following examples ofservices:

-   -   Session setup/teardown    -   Validation (refer to the GDG validation section for details)    -   Channel bonding (aggregation of radio channels into a        super-channel for higher throughput)

Before IP packets are encapsulated inside PDP data messages, they may beoptionally compressed using Lempel-Ziv (LZ) and encrypted using 128-bitTriple-Data Encryption Standard (Triple-DES) technology or equipmentalgorithms. This provides higher throughput for uncompressed data andadds an extra layer of security to the radio link portion of thenetwork.

In order to provide IP addresses to equipment connected to the ADSairborne LAN, a network address translation (NAT) scheme may be used.With NAT a set of IP addresses for multiple hosts are translated into asingle IP address by a NAT router. The GDG acts as the NAT router inthis embodiment. The onboard equipment can be assigned unique (butpublicly unroutable) IP addresses which, when passed through the GDGproxy, are translated into the routable address of the GDG. In thisrespect, hosts outside of the present invention network (i.e., Internet)will believe that a single routable host (the GDG) is responsible forall traffic from the present invention network.

In order to provide mapping from the single IP address of the GDG to themultiple IP addresses of the onboard hosts, a correlation may be madebetween source IP+PORT number and the translated IP+PORT.

For instance, imagine two airborne host applications with source IP+PORTof 10.0.0.1+5000 and 10.0.0.2+5000 respectively. These may be mappedinto source IP+PORT of 11.0.0.1+6000 and 11.0.0.1+6001. Hence a singleGDG (with IP address of 11.0.0.1) can route returning IP packets to theproper onboard host by consulting a table which tracks this translation.

Virtual Private Networks (VPNs) allow for private point-to-point datasessions across public data networks. A variety of proposed standardssuch as layer 2 tunneling protocol (L2TP) or point-to-point tunnelingprotocol (PPTP) provide this service. In the context of the presentinvention network, a VPN allows the end user to access hosts beyond theedge servers (ADS and GDG) as if they were integral parts of theirnetwork. For instance, an onboard server can be made a trusted hostwithin a groundbased network even though data is routed over a sharedpresent invention network.

A key attribute of the present invention network is the ability topresent a seamless network layer to the end applications. To accomplishthis in the mobile radio environment requires a mechanism for switchingthe airborne radio between different ground stations.

The NATS airborne radio constantly monitors metrics such as the receivedsignal quality, Doppler shift, and bit-error-rate (BER) of the radiolink. If one or more of these metrics fall below a configurablethreshold, the airborne radio retunes its transceiver to another groundstation with a better signal such that acceptable data transfer can bemaintained.

In order to reach an airborne radio, the GDG must track which groundstation an airborne radio is currently tuned to. One method foraccomplishing this entails requiring each NATS radio set to register ateach new ground station as it is selected. The process of registeringconsists of a short burst of traffic that identifies the airline andaircraft ID numbers of the airborne radio. The ground station relaysthis information along with its own identifier to the GDG. With thisinformation in hand, the GDG can determine which ground station to routedata through for a particular ADS.

Using the location tracking information, the GDG is able to page aparticular airborne radio. It merely sends a page request to the groundstation that a NATS radio set is known to be registered to. This page isthen forwarded to the NATS radio set using the ground station's pilotchannel. Upon realization that the page is addressed to it, the NATSradio set acts upon the page by seizing a radio channel and setting up apath (also referred to as a radio or data link) for subsequent datatransfer. At this point, the network behaves as if the ADS (rather thanthe GDG) had initiated the request for a data path.

Another embodiment of the present invention utilizes an asymmetric datatransfer technique. This embodiment is well suited to many applications.For instance, world-wide-web traffic is asymmetric in nature. The backchannel from the client to the web server typically requires very littlebandwidth. The information in this direction consists of URLs andacknowledgment packets. However, traffic on the forward channel canoften be very bandwidth intensive (graphics, large documents, etc.).

In the context of the present invention network, the implementation isreadily apparent. The back channel would make use of the presentinvention network while the forward channel could use one of theemerging high bandwidth systems. This enables previously unpracticalapplications such as passenger Internet access, streaming audio/video,etc.

In yet another embodiment of the present invention, voice traffic istransported over IP. Using compression algorithms, speech is encodedinto packets which are transported over an IP network. Products thatmake use of this technology are currently available for use over theInternet. This embodiment provides an efficient alternative for voicecommunications to and from the aircraft.

In one example of how the present invention network may be applied, ahigh quality weather map may be delivered to the flight deck. FIG. 6illustrates an example of the flow of data involved in delivering aweather map to an airborne applications terminal aboard a subscribingaircraft in accordance with the present invention. The weather map isfirst retrieved from a pre-arranged source (possibly from a serverconnected to the Internet 601 or a dedicated connection to an electronicmap warehouse). The map is then cached on the GDG 602 so that, ifmultiple aircraft request the same file, the GDG needn't duplicate theretrieval effort. Next the map is transferred (using FTP) from the GDGto the ADS 606. In doing so the file traverses the WAN 603, GroundStation 604, and NATS Radio set 605. Finally the file can be transferredto the Airborne Applications Terminal 607 for final display (usingperhaps a web browser). Airborne Applications Terminal 607 may be, forexample, a crew or flight deck general purpose computer 214 asillustrated in FIG. 2.

The weather map application can work in either a push or pull fashion.In the push scenario, the map is sent to the aircraft based on apredetermined rule set (perhaps time of day, aircraft routing, etc.). Inthe pull case, the ADS requests the map based on either a pre-determinedrule set or interaction from the end user of the Airborne ApplicationsTerminal.

In another example of how the present invention may be applied, aircraftdata may be sent to the dispatch. Examples of this data include thefollowing: engine data, aircraft attitude data, engine speed/temperaturedata, weight on wheels data, and the time the aircraft doors are openedor closed. FIG. 7 illustrates an example of the flow of data involved indelivering data from a subscribing aircraft to the dispatch inaccordance with the present invention. First, an aircraft system ordevice 701 sends the data to the ADS 702. The aircraft system or device701 may be (for example) an aircraft discrete, a relay, a switch, anaircraft BUS, a piece of avionics equipment, an ACMS system, or an ACARSMU. The ADS 702 may process the received data prior to encapsulating thedata into packets and sending the data packets to the NATS radio set703. For example, the ADS 702 may process the data to generate an ACMSreport which indicates which data parameters are outside ofpredetermined parameters.

The NATS radio set 703 then transmits the data packets to a groundstation 704. Ground station 704 then sends the data packets to the GDG706 via WAN 705. GDG 706 may then route the data to a general purposecomputer 707 at the dispatch location after removing the encapsulation.

In another example of how the present invention may be applied, flightmanagement system software updates may be sent from a dispatch locationto avionics equipment aboard the aircraft. In this application, the dataessentially follows the reverse of the flow described above with respectto FIG. 7. The aircraft device 701 may be any piece of avionicsequipment aboard the aircraft requiring data or software updates. TheADS 702 may send the data update to the intended avionics equipmentusing a known protocol such as ARINC 615.

In another example of how the present invention may be applied, apassenger or crew member may exchange data with a ground-based computerconnected to a network. The passenger may wish to access a serverconnected to an office LAN or access an Internet Web site supported by aserver connected to the Internet. The crew may wish to notify dispatchthat a piece of equipment on the aircraft needs repair/replacement. FIG.8 illustrates an example of the flow of data involved in exchanging databetween a laptop utilized by a passenger or crew member and aground-based computer. For the air-to-ground transmission, the passengeror crew member uses a general purpose computer 801 to send data or aquery to the ADS 802. General purpose computer 801 may be a laptopcomputer connected to an existing telephone handset as illustrated inFIG. 2. The ADS encapsulates the data or query into packets and sendsthe data packets to the NATS radio set 803. The data packets then followa path to GDG 806 via ground station 804 and WAN 805 as described above.GDG 806 removes the encapsulation, if necessary, and then routes thedata or query to destination computer 808 via network 807. Network 807may be, for example the Internet. Destination computer 808 may bedirectly connected to GDG 806 rather than through a network such asnetwork 807. The flow of data from destination computer 808 back togeneral purpose computer 801 follows the reverse of these steps.

As described above, the present invention may be applied to enable anairline passenger or crew member to make a voice telephone call tosomeone on the ground. FIG. 9 illustrates an example of the flow of datainvolved in completing a telephone call in accordance with the presentinvention. Voice information or a call initiation request is sent fromtelephone handset 901 to ADS 902. ADS 902 encapsulates the received dataand sends the data packets to NATS radio set 903. The data packetstraverse ground station 904 and WAN 905 to arrive at GDG 906 asdescribed above. GDG 906 then removes the encapsulation, if necessary,and routes the data packets to audio transceiver device 908 via anetwork 907. Network 907 may be a PSTN or an IP network. Audiotransceiving device 908 may be, for example, a telephone connected tothe PSTN, a wireless telephone communicating with a PSTN or an IPnetwork, or a general purpose computer adapted to process IP voicepackets and connected to an IP network. Voice data from audiotransceiving device 908 follows the reverse of the above described dataflow.

Although several embodiments are specifically illustrated herein, itwill be appreciated that modifications and variations of the presentinvention are covered by the above teachings and within the purview ofthe appended claims without departing from the spirit and intended scopeof the invention. For example, the above described methods may beadapted to transmit data between a subscribing aircraft and aground-based device via a satellite when the subscribing aircraft is outof range of the plurality of ground stations. In a manner similar tothat described above with reference to airline passengers or crewmembers initiating telephone calls from the aircraft to a ground-basedtelephone device, the present invention is also intended to permitairline passengers or crew members aboard the aircraft to receivetelephone calls initiated from a ground-based telephone device.

1.-47. (canceled)
 48. A method for providing data communicationsservices utilizing a network comprising a first server adapted to beconnected to a North American Terrestrial System (NATS) radio set and asecond server adapted to be connected to a plurality of ground stations,wherein data packets are exchanged between an application programrunning on the first server and an application program running on thesecond server via a wireless connection between the NATS radio set andat least one of the plurality of ground stations, and wherein both thefirst server and the second server are adapted to transmit data to andreceive data from devices outside the network, the method comprising thesteps of: receiving, at the first server, data from a first device;encapsulating the data in accordance with a first protocol; and sendingsaid encapsulated data to the NATS radio set.
 49. The method of claim48, wherein said first protocol is transmission controlprotocol/Internet protocol (TCP/IP).
 50. The method of claim 49, whereinthe data is analog voice data received via a telephone handset.
 51. Themethod of claim 49, wherein the data is aircraft condition monitoringsystem (ACMS) data received from several sources; and further comprisingthe steps of: comparing the received ACMS data to predetermined values;and generating reports summarizing a result of said comparing step. 52.The method of claim 49, wherein the data is Aircraft CommunicationAddressing and Reporting System Management system (ACARS MU) data;wherein said first device is one of a relay, a switch on an aircraft,and an aircraft bus.
 53. The method of claim 49, wherein the data isanalog voice information; and wherein said first device is a telephonehandset.
 54. The method of claim 49, wherein said first device is one ofa general purpose computer and a laptop computer.
 55. A method forproviding data communications services utilizing a network comprising afirst server adapted to be connected to a North American TerrestrialSystem (NATS) radio set and a second server adapted to be connected to aplurality of ground stations, wherein data packets are exchanged betweenan application program running on the first server and an applicationprogram running on the second server via a wireless connection betweenthe NATS radio set and at least one of the plurality of ground stations,and wherein both the first server and the second server are adapted totransmit data to and receive data from devices outside the network, themethod comprising the steps of: receiving, from the NATS radio set, dataencapsulated into packets in accordance with a first protocol; removingsaid data from said encapsulated packets, if necessary; storing the datawithin a memory device adapted to be connected to the first server, ifnecessary; encapsulating the data in accordance with a second protocol,if necessary; and sending one of said received data packets, the data,and said data encapsulated in accordance with said second protocol to afirst device.
 56. The method of claim 55, wherein said first protocol istransmission control protocol/Internet protocol (TCP/IP).
 57. The methodof claim 56, wherein the data is analog voice data received by the NATSradio set via one of a public switched telephone network (PSTN) and anInternet protocol (IP) network; and wherein said first device is atelephone handset.
 58. The method of claim 56, wherein said first deviceis one of a general purpose computer and a laptop computer.
 59. Themethod of claim 56, wherein the data is flight management systemsoftware update information; and wherein said first device is a piece ofavionics equipment. 60.-67. (canceled)
 68. A computer-readable mediumwhose contents cause a computer system to transmit data from a firstdevice to a second device utilizing a network comprising a first serveradapted to be connected to a North American Terrestrial System (NATS)radio set and a second server adapted to be connected to a plurality ofground stations, wherein data packets are exchanged between anapplication program running on the first server and an applicationprogram running on the second server via a wireless connection betweenthe NATS radio set and at least one of the plurality of ground stations,and wherein both the first server and the second server are adapted totransmit data to and receive data from devices outside the network, byperforming the steps of: receiving, at the second server, the data fromthe first device; encapsulating the data into packets in accordance witha first protocol using the second server; determining which one of aplurality of ground stations is currently serving the North AmericanTerrestrial System (NATS) radio set associated with the second device;sending said data packets to said determined ground station;transmitting said data packets from said determined ground station tothe determined NATS radio set; sending said data packets from the NATSradio set to the first server; removing the data from said firstprotocol encapsulated packets using the first server, if necessary;encapsulating the data in accordance with a second protocol, using saidfirst server, if necessary; and sending one of said data packets, thedata, and said data encapsulated in accordance with said second protocolfrom the first server to the second device.
 69. The computer-readablemedium of claim 68, wherein the second server is a ground data gateway(GDG), wherein the first server is an airborne data server (ADS), andwherein said first protocol is transmission control protocol/Internetprotocol (TCP/IP).
 70. The computer-readable medium of claim 68, whereinthe step of transmitting said data packets further comprises the stepsof: transmitting a page message to said determined NATS radio set usingboth said determined ground station and a predetermined channel, saidpage message indicating to said determined NATS radio set that saidground station intends to transmit data packets to said determined NATSradio set; seizing a system channel using said NATS radio set inresponse to said page message; and establishing a radio link fortransmitting data between said NATS radio set and said determined groundstation using said seized system channel.
 71. A computer-readable mediumwhose contents cause a computer system to provide data communicationsservices utilizing a network comprising a first server adapted to beconnected to a North American Terrestrial System (NATS) radio set and asecond server adapted to be connected to a plurality of ground stations,wherein data packets are exchanged between an application programrunning on the first server and an application program running on thesecond server via a wireless connection between the NATS radio set andat least one of the plurality of ground stations, and wherein both thefirst server and the second server are adapted to transmit data to andreceive data from devices outside the network, by performing the stepsof: receiving, at the first server, data from a first device;encapsulating the data in accordance with a first protocol; and sendingsaid encapsulated data to the NATS radio set.
 72. The computer-readablemedium of claim 71, wherein said first protocol is transmission controlprotocol/Internet protocol (TCP/IP).
 73. A computer-readable mediumwhose contents cause a computer system to provide data communicationsservices utilizing a network comprising a first server adapted to beconnected to a North American Terrestrial System (NATS) radio set and asecond server adapted to be connected to a plurality of ground stations,wherein data packets are exchanged between an application programrunning on the first server and an application program running on thesecond server via a wireless connection between the NATS radio set andat least one of the plurality of ground stations, and wherein both thefirst server and the second server are adapted to transmit data to andreceive data from devices outside the network, by performing the stepsof: receiving, from the NATS radio set, data encapsulated into packetsin accordance with a first protocol; removing said data from saidencapsulated packets, if necessary; storing the data within a memorydevice adapted to be connected to the first server, if necessary;encapsulating the data in accordance with a second protocol, ifnecessary; and sending one of said received data packets, the data, andsaid data encapsulated in accordance with said second protocol to afirst device.
 74. (canceled)
 75. The computer-readable medium of claim73, wherein the first protocol is a Transmission ControlProtocol/Internet Protocol (TCP/IP).
 76. The computer-readable medium ofclaim 75, wherein the data is analog voice data recorded via a telephonehandset.